The Collaborative International Dictionary of English v.0.48:

Pharos \Pha"ros\, n. [L., fr. Gr. fa`ros, fr. Fa`ros an island
   in the Bay of Alexandria, where king Ptolemy Philadelphus
   built a famous lighthouse, one of the seven wonders of the
   ancient world.]
   A lighthouse or beacon for the guidance of seamen.
   [1913 Webster]

         He . . . built a pharos, or lighthouse.  --Arbuthnot.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pharos
    n 1: a tower with a light that gives warning of shoals to
         passing ships [syn: beacon, lighthouse, beacon light,
         pharos]